Comparison of Degradation on Aluminum Reflectors for Solar Collectors due to Outdoor Exposure and Accelerated Aging

Johannes Wette,Stefan Ziegler,Aránzazu Fernández-García,Reinhard Dasbach,Florian Sutter

doi:10.3390/en9110916

Abstract

Reflectors for concentrated solar thermal technologies need to withstand 20 or even 30 years of outdoor exposure without significant loss of solar specular reflectance. In order to test the durability of innovative reflectors within a shorter period of time, an accelerated aging methodology is required. The problem with accelerated testing is that poor correlation between laboratory and field test results has been achieved in the past. This is mainly because unrealistic degradation mechanisms are accelerated in the weathering chambers. In order to define a realistic testing procedure, a high number of accelerated aging tests have been performed on differently coated aluminum reflectors. The degradation mechanisms of the accelerated tests have been classified and systematically compared to samples that have been exposed at nine different exposure sites outdoors. Besides the standardized aging tests, innovative aging procedures have been developed in such way that the agreement to the degradation pattern observed outdoors is increased. Although degradation depends on materials and location, five generic degradation mechanisms were detected. Standardized tests only reproduced one or two of the five mechanisms detected outdoors. Additionally, several degradation effects that were not observed outdoors appeared. The innovative accelerated aging tests of artificially soiled samples were able to reproduce three of the five mechanisms observed outdoors, presenting a much more realistic overall degradation pattern.

Highlights

IntroductionIndustry is one of the main consumers of energy worldwide, around 30% [1], with direct thermal energy (known as industrial process heat, IPH) representing a large share of this energy demand in many sectors [2]
Industry is one of the main consumers of energy worldwide, around 30% [1], with direct thermal energy representing a large share of this energy demand in many sectors [2]
The five main degradation mechanisms that were detected during the outdoor testing campaign are the following:

Summary

Introduction

Industry is one of the main consumers of energy worldwide, around 30% [1], with direct thermal energy (known as industrial process heat, IPH) representing a large share of this energy demand in many sectors [2]. As the temperature requirements of IPH applications range from 60 ◦ C to 260 ◦ C [3], concentrating solar thermal systems are becoming essential for covering such thermal energy demand with renewable energies [4]. These small-sized concentrating solar thermal systems (including small-sized parabolic-trough collectors, PTC, compound parabolic concentrators, CPC, and solar cookers) are important for the thermal energy supply in sustainable cities, isolated locations and rural areas, covering applications such as for solar cooking [5,6], domestic hot water, space heating, pumping irrigation water, desalination and water treatment [7]. Lifetime goals for reflector materials range up to 20 or even 30 years as demanded by the industry [12]

Methods

Results

Conclusion